re PR target/81708 (The x86 stack canary location should be customizable)

	PR target/81708
	* config/i386/i386.opt (mstack-protector-guard-symbol=): New option
	* config/i386/i386.c (ix86_stack_protect_guard): Use
	ix86_stack_protect_guard_symbol_str to generate varible declaration.
	* doc/invoke.texi (x86 Options): Document
	-mstack-protector-guard-symbol= option.

testsuite/ChangeLog:

	PR target/81708
	* gcc.target/i386/stack-prot-sym.c: New test.

From-SVN: r251040

6 files changed, 71 insertions, 9 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index f210597..c73897f 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,14 @@
 2017-08-10  Uros Bizjak  <ubizjak@gmail.com>
 
+	PR target/81708
+	* config/i386/i386.opt (mstack-protector-guard-symbol=): New option
+	* config/i386/i386.c (ix86_stack_protect_guard): Use
+	ix86_stack_protect_guard_symbol_str to generate varible declaration.
+	* doc/invoke.texi (x86 Options): Document
+	-mstack-protector-guard-symbol= option.
+
+2017-08-10  Uros Bizjak  <ubizjak@gmail.com>
+
 	* config/i386/i386-protos.h (ix86_split_stack_guard): New prototype.
 	* config/i386/i386.c (ix86_split_stack_guard): New function.
 	(ix86_xpand_split_stack_prologue): Call ix86_split_stack_guard.
diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index 9d59c78..1135372 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -45854,21 +45854,55 @@ ix86_mangle_type (const_tree type)
     }
 }
 
+static GTY(()) tree ix86_tls_stack_chk_guard_decl;
+
 static tree
 ix86_stack_protect_guard (void)
 {
   if (TARGET_SSP_TLS_GUARD)
     {
       tree type_node = lang_hooks.types.type_for_mode (ptr_mode, 1);
-
       int qual = ENCODE_QUAL_ADDR_SPACE (ix86_stack_protector_guard_reg);
-
       tree type = build_qualified_type (type_node, qual);
-      tree asptrtype = build_pointer_type (type);
-      tree sspoff = build_int_cst (asptrtype,
-				   ix86_stack_protector_guard_offset);
-      tree t = build2 (MEM_REF, asptrtype, sspoff,
-		       build_int_cst (asptrtype, 0));
+      tree t;
+
+      if (global_options_set.x_ix86_stack_protector_guard_symbol_str)
+	{
+	  t = ix86_tls_stack_chk_guard_decl;
+
+	  if (t == NULL)
+	    {
+	      rtx x;
+
+	      t = build_decl
+		(UNKNOWN_LOCATION, VAR_DECL,
+		 get_identifier (ix86_stack_protector_guard_symbol_str),
+		 type);
+	      TREE_STATIC (t) = 1;
+	      TREE_PUBLIC (t) = 1;
+	      DECL_EXTERNAL (t) = 1;
+	      TREE_USED (t) = 1;
+	      TREE_THIS_VOLATILE (t) = 1;
+	      DECL_ARTIFICIAL (t) = 1;
+	      DECL_IGNORED_P (t) = 1;
+
+	      /* Do not share RTL as the declaration is visible outside of
+		 current function.  */
+	      x = DECL_RTL (t);
+	      RTX_FLAG (x, used) = 1;
+
+	      ix86_tls_stack_chk_guard_decl = t;
+	    }
+	}
+      else
+	{
+	  tree asptrtype = build_pointer_type (type);
+
+	  t = build_int_cst (asptrtype, ix86_stack_protector_guard_offset);
+	  t = build2 (MEM_REF, asptrtype, t,
+		      build_int_cst (asptrtype, 0));
+	}
+
       return t;
     }
 
diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt
index 72f2422..cd56431 100644
--- a/gcc/config/i386/i386.opt
+++ b/gcc/config/i386/i386.opt
@@ -938,6 +938,10 @@ Use the given offset for addressing the stack-protector guard.
 TargetVariable
 HOST_WIDE_INT ix86_stack_protector_guard_offset = 0
 
+mstack-protector-guard-symbol=
+Target RejectNegative Joined Integer Var(ix86_stack_protector_guard_symbol_str)
+Use the given symbol for addressing the stack-protector guard.
+
 mmitigate-rop
 Target Var(flag_mitigate_rop) Init(0)
 Attempt to avoid generating instruction sequences containing ret bytes.
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 3753d8a..ec29f1d 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -1216,7 +1216,8 @@ See RS/6000 and PowerPC Options.
 -mavx256-split-unaligned-load  -mavx256-split-unaligned-store @gol
 -malign-data=@var{type}  -mstack-protector-guard=@var{guard} @gol
 -mstack-protector-guard-reg=@var{reg} @gol
--mstack-protector-guard-offset=@var{offset}  -mmitigate-rop @gol
+-mstack-protector-guard-offset=@var{offset} @gol
+-mstack-protector-guard-symbol=@var{symbol} -mmitigate-rop @gol
 -mgeneral-regs-only  -mcall-ms2sysv-xlogues}
 
 @emph{x86 Windows Options}
@@ -22757,9 +22758,11 @@ The @option{-mno-compat-align-parm} option is the default.
 @item -mstack-protector-guard=@var{guard}
 @itemx -mstack-protector-guard-reg=@var{reg}
 @itemx -mstack-protector-guard-offset=@var{offset}
+@itemx -mstack-protector-guard-symbol=@var{symbol}
 @opindex mstack-protector-guard
 @opindex mstack-protector-guard-reg
 @opindex mstack-protector-guard-offset
+@opindex mstack-protector-guard-symbol
 Generate stack protection code using canary at @var{guard}.  Supported
 locations are @samp{global} for global canary or @samp{tls} for per-thread
 canary in the TLS block (the default with GNU libc version 2.4 or later).
@@ -22769,7 +22772,8 @@ With the latter choice the options
 @option{-mstack-protector-guard-offset=@var{offset}} furthermore specify
 which register to use as base register for reading the canary, and from what
 offset from that base register. The default for those is as specified in the
-relevant ABI.
+relevant ABI.  @option{-mstack-protector-guard-symbol=@var{symbol}} overrides
+the offset with a symbol reference to a canary in the TLS block.
 @end table
 
 @node RX Options
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index da63e03..3100618 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2017-08-10  Uros Bizjak  <ubizjak@gmail.com>
+
+	PR target/81708
+	* gcc.target/i386/stack-prot-sym.c: New test.
+
 2017-08-10  Richard Sandiford  <richard.sandiford@linaro.org>
 
 	PR testsuite/81738
diff --git a/gcc/testsuite/gcc.target/i386/stack-prot-sym.c b/gcc/testsuite/gcc.target/i386/stack-prot-sym.c
new file mode 100644
index 0000000..7f63424
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/stack-prot-sym.c
@@ -0,0 +1,6 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fstack-protector-all -mstack-protector-guard=tls -mstack-protector-guard-reg=gs -mstack-protector-guard-symbol=my_guard" } */
+
+void f(void) { }
+
+/* { dg-final { scan-assembler "gs:my_guard" } } */